Sotalol

Sotalol is what is called a non-cardioselective beta-blocker: it blocks both the beta-1 and beta-2 adrenergic receptors, the ones through which adrenaline speeds up and strengthens the heart. By occupying them, it slows the heart rate and dampens electrical conduction, which corresponds to the class II effect in the Vaughan-Williams classification. This first action calms a heart that beats too fast and reduces the muscle’s sensitivity to surges of adrenaline.

Sotalol has a second action, less common among beta-blockers, which defines its class III. It blocks the rapid delayed rectifier potassium current, called IKr, carried by the Kv11.1 channel (also known as HERG). By slowing the exit of potassium from the cells, it lengthens the duration of the action potential and the effective refractory period in the atrium, the Purkinje fibres and the ventricle. This prolonged repolarisation appears on the electrocardiogram as a lengthened QT interval: it carries the drug’s antiarrhythmic effect, but also explains its risk of torsades de pointes.

Sotalol is intended for serious rhythm disorders. It treats severe ventricular tachycardias, provided they are haemodynamically stable, meaning that circulation is maintained during the episode. Its dual action, slowing the heart and lengthening the refractory period, breaks the abnormal electrical circuits that sustain these dangerous accelerations arising from the ventricles.

Its second major indication concerns the atrium: maintaining sinus rhythm, that is the normal rhythm, in patients who have already experienced symptomatic atrial fibrillation or flutter. Once regular rhythm is restored, sotalol aims to prevent the arrhythmia from returning. In both cases, this is a long-term treatment that the cardiologist starts and adjusts with care, often under hospital monitoring at the outset.

Sotalol is very well absorbed by mouth, with a bioavailability of 90 to 100 %. A standard meal does, however, reduce its absorption by about 20 % compared with taking it on an empty stomach. The rule is therefore consistency: always take it the same way, either always with food or always without, and at regular times. Antacids based on aluminium and magnesium hydroxide lower its peak concentration by about 26 % and its exposure by about 20 %, so they should be separated from the dose by at least 2 hours.

The elimination half-life of sotalol is about 12 hours, which explains the usual twice-daily dosing, morning and evening. The drug is not transformed by the liver and does not bind to blood proteins: it leaves the body almost entirely through the kidney, unchanged. This elimination route means the dose must be reduced when kidney function declines. One point is worth remembering: you do not stop sotalol on your own initiative, because abruptly interrupting a beta-blocker can destabilise the heart; any change goes through the doctor.

The most common effects stem from the slowing of the heart and the beta-blocking action. In trials conducted at doses of 160 to 240 mg per day and compared with a placebo, fatigue affects 19.6 % of patients versus 8.5 %, and dizziness 16.3 % versus 12.4 %. Bradycardia, that is an abnormally slow pulse, concerns 13.1 % of patients versus 2.5 %, and shortness of breath 9.2 % versus 7.4 %. Digestive disturbances are also frequent: nausea or vomiting in 7.8 % of patients versus 5.3 %, and diarrhoea in 5.2 % versus 2.1 %.

The most feared effect is torsades de pointes, a ventricular rhythm disorder linked to QT prolongation. Its risk depends closely on the dose: it remains about 0.3 % at doses of 320 mg per day or less, but climbs to 3.2 % above 320 mg per day in patients treated for atrial fibrillation or flutter. It is to control this risk that treatment is started gradually, under electrocardiogram monitoring, and that the dosage is adjusted carefully.

Two minerals take centre stage with sotalol, because they weigh directly on the risk of rhythm disorder. A low level of potassium (hypokalaemia) or magnesium (hypomagnesaemia) worsens QT prolongation and increases the risk of torsades de pointes. This is why these levels are corrected before starting treatment, then monitored afterwards: the target is potassium above 4 mEq/L and magnesium above 2 mEq/L, and a potassium level below this threshold contraindicates initiation. Maintaining a good status in these two minerals is therefore part of the ground on which the treatment rests.

The diet naturally contributes to this status. Potassium is abundant in bananas, spinach, sweet potato, dried apricots and legumes. Magnesium is found in pumpkin seeds, almonds, spinach again, dark chocolate and whole grains. These dietary intakes support the intended balance, without ever replacing blood tests or treatment. When daily intake remains irregular or insufficient, a targeted magnesium supplement makes sense, in addition to your treatment and never in its place.

Sotalol does not like the company of other drugs that prolong the QT: combining it with numerous antiarrhythmics, with certain phenothiazines, with tricyclic antidepressants and with certain macrolides is not recommended, because the effects add up on repolarisation. Digoxin and calcium channel blockers can compound their action with its own on atrioventricular conduction and heart rate. Stopping clonidine while a beta-blocker is ongoing exposes the patient to a rebound rise in blood pressure. In diabetics treated with insulin or antidiabetic drugs, sotalol can mask the signs of hypoglycaemia and alter glycaemic control.

Monitoring is organised around two measurements. Creatinine clearance, calculated before the first dose, governs the dosage: two doses a day if it exceeds 60 mL/min, a single dose between 40 and 60 mL/min, and a contraindication below 40 mL/min. The electrocardiogram monitors the QT interval: sotalol is not started if the baseline QTc exceeds 450 ms, and if the QT reaches 500 ms or more during treatment, the dose is reduced or the drug stopped. Added to this is the monitoring of blood potassium and magnesium, corrected before initiation then followed throughout the duration of treatment.